A process for delamination of layered silicates

ABSTRACT

The invention relates to a process for delamination of a layered silicate in an aqueous medium, wherein in a first step a layered silicate is treated with a delamination agent, and in a second step the thus treated layered silicate is contacted with an aqueous medium, whereby the delamination agent is a compound having exactly one positively charged atom, the positively charged atom being selected from the group consisting of nitrogen and phosphorous; contains nf functional groups selected from the group consisting of hydroxyl groups, ether groups, sulfonic acid ester groups and carboxylic acid ester groups, nf being a number from 3 to 10; comprises a total number of carbon atoms nc being from 4 to 12; has a ratio nc/(1+nf) from 1 to 2, wherein nc is the total number of carbon atoms of the delamination agent and nf is the total number of functional groups in the delamination agent as defined under ii.; contains nt atoms selected from the group consisting of carbon, nitrogen, phosphorous, oxygen and sulfur, nt being ≥9; and wherein the delamination agent is used to treat the layered silicate in an amount of at least equal to the cation exchange capacity of the layered silicate. The invention further relates to the thus produced delaminated layered silicates, their use in the production of composite and coating material and as a barrier material. Moreover, the invention relates to compositions containing the thus produced delaminated layered silicates.

The present invention relates to a process for delamination of layeredsilicates in an aqueous environment, the thus produced products and theuse of these products as barrier material, such as a diffusion orflame-proof barrier material for various articles, and particularly incomposite materials.

It is known in the prior art to add layered silicates to surface-coatingcompositions or composite materials. The mechanical properties of theresulting systems can be improved thereby. In particular, it is possiblein that manner to increase the barrier action of a surface-coating orcomposite material layer.

It has been shown that the degree of improvement in the propertiesdepends significantly on the aspect ratio of the platelets thus producedfrom the layered silicates. It is accordingly desirable in principle toproduce platelets having a high aspect ratio, because therewith it ispossible to obtain surface-coating or composite material layers whichare distinguished by particularly good mechanical properties and a highbarrier action. The aspect ratio is understood as being the quotient ofthe platelet length and the height of the platelet. Consequently, bothan increase in the platelet length and a reduction in the plateletheight brings about an increase in the aspect ratio. The theoreticallower limit of the platelet height of layered silicates is a singlesilicate lamella, which in the case of 2:1-clay materials amounts toabout one nanometer.

In general, layered silicates have stacks of silicate lamellae,so-called tactoids, with heights of from several nanometers to a fewmillimeters.

The aspect ratio can be increased within certain limits by chemicaland/or physical treatment, by cleaving the platelets along their stackaxis.

The increase in the aspect ratio which accompanies an exfoliation isregarded, for example, as being an important condition to producepolymer-phyllosilicate nanocomposites having improved properties (H. A.Stretz, D. R. Paul, R. Li, H. Keskkula, P. E. Cassidy, Polymer 2005, 46,2621-2637 and L. A. Utracki, M. Sepehr, E. Boccaleri, Polymers forAdvanced Technologies 2007, 18, 1-37).

A disadvantage in the processing of known layered silicates are their insome cases contradictory properties. For example, it is known thathydrothermally produced smectites exhibit extremely good swellingbehavior, because of which spontaneous exfoliation into individualsilicate lamellae may be achieved. However, such smectites have smallplatelet diameters of about 50 nanometers, so that the aspect ratios donot exceed a value of 50.

Although natural phyllosilicates of the montmorillonite or vermiculitetype exhibit platelet diameters of from several hundred nanometers to afew micrometers, spontaneous delamination does not occur. However, theaspect ratio can be increased by complex exfoliation steps.

In patent and scientific literature, the terms “delamination” and“exfoliation”, with respect to the degree of separating layers of alayered silicate are not used in a consistent manner. As used herein theterm “delamination” refers to separating the layers of a layeredsilicate into individual silicate lamellae, while “exfoliation” refersto separating of layers mainly in stacks of silicate lamellae.

The aspect ratio can either be maximized by maximizing the diameter ofthe platelet or by minimizing its height, or both. While the diameter ofindividual lamellae highly depends on the type of layered silicate andits layer charge, the height of a single silicate lamella of a 2:1-claymaterial is rather constant and about one nanometer as stated above.Therefore, it should always be the aim to minimize the height ofplatelet, i. e. to obtain individual silicate lamellae by delamination.

Therefore, it is an aim of the present invention to provide a processallowing rather a delamination of layered silicates into single lamellaethan an exfoliation of the layered silicates to stacks of lamellae.

The problem is that in many known delamination procedures rathermixtures comprising single lamellae and stacks of lamellae are produced.Therefore, there is a need to provide a purposive way to delaminatelayered silicates into mainly single lamellae by following simple rulesin the selection of a suitable delamination agent in view of a specificlayered silicate which is to be delaminated.

It is particularly difficult to delaminate such layered silicates havinga heterogeneous layer charge distribution, as is the case for somenaturally occurring layered silicates. While some delamination agentsmay be apt to delaminate layered silicates having a high layer chargethe same delamination agent may fail for low layer charges. Therefore,if different regions of layer charges are present in a layered silicate,such delamination agents will fail to completely delaminate the layeredsilicate.

Therefore, there is a big need to provide universal delamination agents,which successfully delaminate layered silicates having regions withdifferent layer charges from high to low layer charges.

Even if a layered silicate has a homogeneous layer charge distribution,such universal delamination agents can be advantageously used, becausethere is no need to know the exact layer charge of the layered silicateto be delaminated to select an appropriate delamination agent.

Furthermore, such universal delamination agent can be successfully usedwith mixtures of different layered silicates each having a ratherhomogeneous layer charge distribution, which however differs from thelayer charges of the other layered silicates in the mixture. In suchcase a mixture comprising layered silicates having different layercharges can still be treated with one and the same delamination agent.

Therefore, it was the aim of the present invention to provide a processfor delamination of a layered silicate by a universal delaminationagent.

The aim of the present invention can be achieved by providing a processfor delamination of a layered silicate in an aqueous medium, wherein

-   -   (A) in a first step        -   a. a layered silicate is treated with        -   b. a delamination agent, and    -   (B) in a second step        -   the thus treated layered silicate obtained in the first step            is contacted with an aqueous medium, characterized in that        -   the delamination agent            -   i. is a compound having exactly one positively charged                atom, the positively charged atom being selected from                the group consisting of nitrogen and phosphorous;            -   ii. contains n_(f) functional groups selected from the                group consisting of hydroxyl groups, ether groups,                sulfonic acid ester groups and carboxylic acid ester                groups, n_(f) being a number from 3 to 10;            -   iii. comprises a total number of carbon atoms n_(c)                being from 4 to 12;            -   iv. has a ratio n_(c)/(1+n_(f)) from 1 to 2, wherein                n_(c) is the total number of carbon atoms of the                delamination agent and n_(f) is the total number of                functional groups in the delamination agent as defined                under ii.;            -   v. contains n_(t) atoms selected from the group                consisting of carbon, nitrogen, phosphorous, oxygen and                sulfur, n_(t) being ≥9; and wherein                the delamination agent is used to treat the layered                silicate in an amount of at least equal to the cation                exchange capacity of the layered silicate.

The term “a layered silicate” also encompasses a mixture of layeredsilicates.

The suitable delamination agents are described by their chemicalproperties i. to iv. encompassing clear structural specificationsregarding the number of positively charged nitrogen or phosphorousatoms, the occurrence of different, rather hydrophilic functionalgroups, their molecular size by means of the number of carbon atoms andthe degree of hydrophilicity by means of a ratio of carbon atoms tohydrophilic functional groups and positively charged nitrogen orphosphorous atoms.

The above process gives the clear instruction how to obtain a reliablehigh degree of delamination of a layered silicate, even for layeredsilicates having different layer charges or regions of different layercharges within one layered silicate.

The degree of delamination preferably being ≥80 wt.-%, more preferablybeing ≥90 wt.-% and most preferably being ≥95 wt.-% of the total weightof treated layered silicate. The degree of delamination can bedetermined by using a 1 wt.-% suspension of the treated clay suspension,centrifuging the clay suspension for 6 min at 4000 g and subsequentlydetermining the dry mass of the delaminated gel m_(d) (in thesupernatant) and the dry mass of the sediment m_(s). The relationm_(d)/(m_(d)+m_(s)) in percent is the degree of delamination. The drymasses are determined by drying the sample at 80° C. until no change inweight is observed.

The process for delamination of a layered silicate according to thepresent invention is also a process for producing individual silicatelamellae from layered silicates.

DETAILED DESCRIPTION

In the following, the present invention will be described in moredetail, particularly with respect to further preferred embodiments ofspecific features.

Layered Silicates

Preferably the layered silicates have a layer charge L_(c) from ≥0.25 to≤1.0 and a charge equivalent area A_(s)=47.6 Å²/(2 L_(c)). If the layercharge is heterogeneous, it is preferred if the layer charges of thedifferent regions of layer charges within a layered silicate are in theabove range. The same applies, if mixtures of different layeredsilicates with homogeneous but different layer charges are to bedelaminated. Layer charges L_(c) are given per formula unit (p.f.u.) ofSi₄O₁₀F₂. A_(s) is given in Å²/charge.

Preferred layered silicates to be used in the present invention areso-called 2:1-clay minerals, particularly preferred are smectites andvermiculites.

Most preferred layered silicates as to be used in the process accordingto the present invention can be depicted by general formula (I)

[M _(Lc/valency)]^(inter)[M ^(I) _(m) M ^(II) _(o)]^(oct)[M ^(III)₄]^(tet) x ₁₀ Y ₂  (I)

wherein,M are metal cations of oxidation state 1 to 3;M^(I) are metal cations of oxidation state 2 or 3;M^(II) are metal cations of oxidation state 1 or 2;M^(III) are atoms of oxidation state 4;X are di-anions;Y are mono-anions;m is ≤2.0 for metal atoms M^(I) of oxidation state 3 andm is ≤3.0 for metal atoms M^(I) of oxidation state 2;o is ≤1.0; andthe layer charge L_(c) is ≥0.25 and ≤1.0.

As generally used, the term “inter” refers to the interlayer containingthe interlayer cations, “tetra” refers to the tetrahedral sheetcontaining the atoms having oxidation state 4 and “octa” refers to theoctahedral sheet containing metal cations M^(I) and/or M^(II).

The range of the layer charge L_(c) encompasses naturally occurring aswell as synthetic layered silicates, particularly such of the smectitetype (L_(c)<0.6) and vermiculite type (L_(c) 0.6).

Synthetic layered silicates are preferably used and preferably preparedby high-temperature melt synthesis, which is optionally followed by anannealing procedure. It is also possible to carry out a layer chargereduction of the as-synthesized or as-annealed layered silicates.

M preferably has oxidation state 1 or 2. M is particularly preferablyLi⁺, Na⁺, Mg²⁺ or a mixture of two or more of those ions.

M^(I) is preferably Mg²⁺, Al³⁺, Fe²⁺, Fe³⁺ or a mixture of two or moreof those ions.

M^(II) is preferably Li⁺, Mg²⁺ or a mixture of those cations.

M^(III) is preferably a tetravalent silicon cation.

X is preferably O²⁻,

Y is preferably OH⁻ or F⁻, particularly preferred F⁻.

The layer charge L_(c) is preferably ≥0.28 and ≤0.95, more preferred≥0.30 and ≤0.90 and most preferred ≥0.35 and ≤0.75.

According to a particularly preferred embodiment of the invention, M isLi⁺, Na⁺, Mg²⁺ or a mixture of two or more of those ions, M^(I) is Mg²⁺,Al³⁺, Fe²⁺, Fe³⁺ or a mixture of two or more of those ions, M^(II) isLi⁺, Mg²⁺ or a mixture of those ions, M^(III) is a tetravalent siliconcation, X is O²⁻ and Y is OH⁻ or F⁻.

The synthetic layered silicates of the formula[M_(Lc/valency)]^(inter)[M^(I) _(m)M^(II) _(o)]^(oct)[M^(III)₄]^(tet)X₁₀Y₂ can be prepared by heating compounds of the desired metals(salts, oxides, glasses) in the stoichiometric ratio in an open orclosed crucible system to form a homogeneous melt and, then cooling themelt again.

In the case of synthesis in a closed crucible system there can be usedas starting compounds alkali salts/alkaline earth salts, alkaline earthoxides and silicon oxides, preferably binary alkali fluorides/alkalineearth fluorides, alkaline earth oxides and silicon oxides, particularlypreferably LiF, NaF, MgF₂, MgO, quartz.

The relative proportions of the starting compounds are then, forexample, from 0.4 to 0.6 mol of F⁻ in the form of the alkali/alkalineearth fluorides per mol of silicon dioxide and from 0.4 to 0.6 mol ofalkaline earth oxide per mol of silicon dioxide, preferably from 0.45 to0.55 mol of F⁻ in the form of the alkali/alkaline earth fluorides permol of silicon dioxide and from 0.45 to 0.55 mol of alkaline earth oxideper mol of silicon dioxide, particularly preferably 0.5 mol of F⁻ in theform of the alkali/alkaline earth fluorides per mol of silicon dioxideand 0.5 mol of alkaline earth oxide per mol of silicon dioxide.

Charging of the crucible is preferably carried out in such a manner thatfirst the more volatile substances, then the alkaline earth oxide andfinally the silicon oxide are weighed in.

Typically, a high-melting crucible made of a metal that is chemicallyinert or slow to react, preferably of molybdenum or platinum, is used.

Before it is closed, the charged, still open crucible is preferablyheated in vacuo at temperatures of from 200° C. to 1100° C., preferablyfrom 400 to 900° C., in order to remove residual water and volatileimpurities. Experimentally, the procedure is preferably such that theupper crucible edge is red-hot while the lower region of the cruciblehas lower temperatures.

A pre-synthesis is optionally carried out in the closedpressure-resistant crucible for from 5 to 20 minutes at from 1700 to1900° C., particularly preferably at from 1750 to 1850° C., in order tohomogenize the reaction mixture.

The heating and the pre-synthesis are typically carried out in ahigh-frequency induction furnace. The crucible is protected fromoxidation by a protecting atmosphere (e.g. argon), reduced pressure or acombination of both measures.

The main synthesis is carried out with a temperature program that isadapted to the material. This synthesis step is preferably carried outin a rotary graphite furnace with horizontal orientation of the axis ofrotation. In a first heating step, the temperature is increased fromroom temperature to from 1600 to 1900° C., preferably from 1700 to 1800°C., at a heating rate of from 1 to 50° C./minute, preferably from 10 to20° C./minute. In a second step, heating is carried out at from 1600 to1900° C., preferably from 1700 to 1800° C. The heating phase of thesecond step lasts preferably from 10 to 240 minutes, particularlypreferably from 30 to 120 minutes. In a third step, the temperature islowered to a value of from 1100 to 1500° C., preferably from 1200 to1400° C., at a cooling rate of from 10 to 100° C./minute, preferablyfrom 30 to 80° C./minute. In a fourth step, the temperature is loweredto a value of from 1200 to 900° C., preferably from 1100 to 1000° C., ata cooling rate of from 0.5 to 30° C./minute, preferably from 1 to 20°C./minute. The reduction in the heating rate after the fourth step toroom temperature takes place, for example, at a rate of from 0.1 to 100°C./minute, preferably in an uncontrolled manner by switching off thefurnace.

The procedure is typically carried out under protecting gas such as, forexample, Ar or N₂.

The layered silicate is obtained in the form of a crystalline,hygroscopic solid after the crucible has been broken open.

In the case of synthesis in an open crucible system, there is preferablyused a glass stage of the general compositionwSiO₂.xM^(a).yM^(b).zM^(c), wherein 5<w<7; 0<x<4; 0≤y<2; 0≤z<1.5 andM^(a), M^(b), M^(c) are metal oxides and M^(a) is other than M^(b) isother than M^(c).

M^(a), M^(b), M^(c) independently of one another can be metal oxides,preferably Li₂O, Na₂O, K₂O, Rb₂O, MgO, particularly preferably Li₂O,Na₂O, MgO. M^(a) is other than M^(b) is other than M^(c).

The glass stage is prepared in the desired stoichiometry from thedesired salts, preferably the carbonates, particularly preferablyLi₂CO₃, Na₂CO₃, and a silicon source such as, for example, siliconoxides, preferably silica. The pulverulent constituents are convertedinto a glassy state by heating and rapid cooling. The conversion iscarried out preferably at from 900 to 1500° C., particularly preferablyat from 1000 to 1300° C. The heating phase in the preparation of theglass stage lasts from 10 to 360 minutes, preferably from 30 to 120minutes, particularly preferably from 40 to 90 minutes. This procedureis typically carried out in a glassy carbon crucible under a protectedatmosphere and/or reduced pressure by means of high-frequency inductionheating. The reduction of the temperature to room temperature is carriedout by switching off the furnace. The resulting glass stage is thenfinely ground, which can be carried out, for example, by means of apowder mill.

Further reactants are added to the glass stage in a weight ratio of from10:1 to 1:10 in order to achieve the desired stoichiometry. Ratios offrom 5:1 to 1:5 are preferred. If necessary, an excess of the readilyvolatile additives of up to 10% can be added. These are, for example,alkali or alkaline earth compounds and/or silicon compounds. Preferenceis given to the use of light alkali and/or alkaline earth fluorides aswell as the carbonates and oxides thereof, as well as silicon oxides.Preference is given to the use of NaF, MgF₂, LiF and/or an annealedmixture of MgCO₃Mg(OH)₂ and silica.

The mixture is then heated above the melting temperature of the eutecticof the compounds used, preferably to from 900 to 1500° C., particularlypreferably to from 1100 to 1400° C. The heating phase lasts preferablyfrom 1 to 240 minutes, particularly preferably from 5 to 30 minutes.Heating is carried out at a heating rate of from 50 to 500° C./minute,preferably at the maximum possible heating rate of the furnace. Coolingafter the heating phase to room temperature is carried out at a rate offrom 1 to 500° C./minute, preferably in an uncontrolled manner byswitching off the furnace. The product is obtained in the form of acrystalline, hygroscopic solid.

The synthesis is typically carried out in a glassy carbon crucible or agraphite crucible under an inert atmosphere. Heating is typicallycarried out by high-frequency induction.

The described process is substantially more economical owing to theenergy-efficient heating by high-frequency induction, the use ofinexpensive starting compounds (a high degree of purity is not required,pre-drying of the starting materials is not required, broader range ofstarting materials such as, for example, advantageous carbonates) and agreatly shortened synthesis time as compared with synthesis in a closedcrucible system and the possibility of multiple use of the crucible.High-temperature melt synthesis in an open crucible system is thereforeparticularly preferred.

The silicates can be annealed in gas-tight crucibles at temperaturesbetween 800° C. and 1200° C. More preferably in range between 1000° C.and 1100° C. for one to 100 days.

Layer charge reduction of as-synthesized silicates can be carried out byion-exchange with Mg²⁺ and heating at 150° C. to 400° C. for 3 h to 48h, most preferably at 250° C. for 24 h.

The layered silicates produced as lined out above and the naturallyoccurring layered silicates can be characterized by general means knownto one of skill in the art. Particularly, the following methods wereused, which are further detailed in the experimental section of thespecification.

As explained above, the process according to the present invention isparticularly suitable for delaminating layered silicates having aheterogeneous layer charge distribution or mixtures of layered silicatespossessing different layer charges. The differences of layer chargeswithin the to be treated layered silicate or mixture of layeredsilicates ΔL_(c) is preferably up to 0.7, or generally up to 0.5 orparticularly up to 0.3 or up to 0.2

The layer charge L_(c) of the layered silicates was determined accordingto Lagaly (see A. R. Mermut, G. Lagaly, Clays Clay Miner. 2001, 49,393-397)

The layer charge L_(c) can be calculated from the cation exchangecapacity and the molecular weight, both determined as lined out above,by means of the following formula (II):

L _(c)=(CEC[mval/100 g]*Mw[g/mol])/(100,000[meal])  (II)

The charge equivalent area A_(s) of the layered silicate can bedetermined according to the following formula (III)

A _(s)=47.6 Å²/(2 L _(c))  (III),

wherein L_(c) is the layer charge as determined above.

Delamination Agent

The delamination agents as used in the process according to the presentinvention are compounds fulfilling the following requirements.

As a first chemical requirement, the delamination agent contains exactlyone positively charged atom, the positively charged atom being selectedfrom the group consisting of nitrogen and phosphorous. Preferably thepositively charged atom is the nitrogen atom of a protonated orquaternized amino group or a phosphorous atom in a phosphonium group,most preferably the positively charged atom being a nitrogen atom.

A second chemical requirement is that the delamination agent contains anumber of n_(f)=3 to 10, preferably 3 to 8, more preferred 3 to 6 andmost preferred 3 to 5 functional groups selected from the groupconsisting of the following four types of groups: hydroxyl groups, ethergroups, sulfonic acid ester groups and carboxylic acid ester groups.Amongst the afore-mentioned groups, hydroxyl groups, ether groups andcarboxylic acid ester groups are preferred, amongst which hydroxyl andether groups are even more preferred. Most preferred are hydroxylgroups. All ranges for n_(f) also apply, if only one type of groups, twotypes of groups or three types of groups are present in the delaminationagent. The functional groups guarantee a minimum extent ofhydrophilicity of the delamination agent beside the positively chargedatom of the above first chemical requirement.

A third chemical requirement is that the delamination agent comprises atotal number of carbon atoms n_(c) being from 4 to 12, preferably 4 to10, more preferably 5 to 9 and most preferably 5 to 7, particularlypreferred 6 or 7. The total number of carbon atoms also includes suchcarbon atoms present in the above functional groups, such as the carbonatoms of a carboxylic acid ester group.

The delamination agent has, as the fourth chemical requirement, a ration_(c)/(1+n_(f)) from 1 to 2, preferably from 1 to 1.8, more preferredfrom 1 to 1.5 and even further preferred from 1 to 1.3 wherein n_(c) isthe total number of carbon atoms of the delamination agent and n_(f) isthe total number of functional groups in the delamination agent asdefined above.

Finally, as a sterical requirement (fifth requirement) the delaminationagent contains n_(t) atoms selected from the group consisting of carbon,nitrogen, phosphorous, oxygen and sulfur, n_(t) being ≥9, more preferredn_(t)≥11 and most preferred n_(t)≥12.

Each of the afore-mentioned four chemical requirements and the onesterical requirement can be realized independently of the otherrequirements in form of its preferred, more and most preferred and evenfurther preferred embodiments as long as the fourth and fifthrequirement are accomplishable. For example, any mandatory requirementcan be combined with a preferred requirement and even a most preferredfurther requirement.

Amongst the delamination agents fulfilling the afore-mentioned fourchemical requirements and one sterical requirement, such delaminationagents are preferred in the process of the present invention having acharge equivalent area A_(d) being from 30 to 90 Å²/charge, which is afurther preferred sterical feature.

More preferred the charge equivalent area A_(d) of the delaminationagent is in the range from 35 to 80 Å² or 40 to 80 Å² and mostpreferably in the range from 45 to 70 Å². A_(d) is given in Å²/charge.

It was found by the present inventors that delamination agent having ann_(t) value and/or a charge equivalent area A_(d) in the above rangesare particularly suitable, even if the layered silicate has aheterogeneous layer charge distribution as is the case for somenaturally occurring layered silicates, such as montmorillonites.

The charge equivalent area of the delamination agent A_(d) is themaximum projection area of the lowest energy conformer, based on the vander Waals radius. It can comfortably be determined online(https://chemicalize.org) or with software solutions as for exampleprovided by ChemAxon Ltd., Budapest Hungary (MarvinSketch (version6.2.2), calculation module developed by ChemAxon; using the GeometricalDescriptor Plugin of the software, the structure was optimized by theimplemented MMFF94 force field;http://www.chemaxon.com/products/marvin/marvinsketch/, 2014).

If the layer charge range (L_(c) range) of the layered silicate ormixture of layered silicates is known, it is possible to furtheroptimize the process by selecting the delamination agent in view of thecharge equivalent area A_(s) of the layered silicate or mixture oflayered silicates to be delaminated. It was found by the presentinventors, that it is particularly preferred if the A_(d)/A_(s) ratio isfrom ≥0.9 to 3.0, more preferred in the range of ≥0.92 to 2.5, even morepreferred in the range from ≥0.92 to 2.0.

Amongst the suitable delamination agents such delamination agents aremost suitable which belong to the group of ionic compounds (i. e.salts), consisting of an anion and a cation, wherein in the cationcontains a protonated or quarternized nitrogen atom or a phosphoniumgroup.

If the cation contains a protonated or quaternized nitrogen atom, theprotonated or quaternized nitrogen atom is preferably the nitrogen atomof an amino polyol, preferably having at least 3 hydroxyl groups. Theamino polyol is even more preferably selected from the group consistingof amino sugars, N-alkyl amino sugars and the same, wherein the C═Ofunctionalities have been reduced to CH—OH functionalities. Suitableexamples for amino sugars are e. g. glucosamine, galactosamine,fructosamine and mannosamine; an N-methylated amino sugar is e.g.N-methyl-D-glucamine. Most preferred are glucosamine andN-methyl-D-glucamine, in their protonated or quaternized forms. Theanions are preferably halide ions such as chloride or iodide.

Detailed Description of the Process Steps

In a first step, according to the process of the present invention, alayered silicate, is treated with a delamination agent. In thistreatment step, the delamination agent is used in an amount which is atleast equal to the cation exchange capacity of the layered silicate.

To carry out the treatment step, preferably an aqueous solution of thedelamination agent is prepared and the layered silicate is suspended inthe aqueous solution of the delamination agent. The concentration of thedelamination agent in the aqueous solution is preferably in the rangefrom 0.2 to 2 mol/L, more preferred in the range of 0.5 to 1.5 mol/L. Ingeneral the concentration of the delamination agent is chosen to be highenough to prevent a premature delamination of the layered silicate atthis stage. The amount of layered silicate is preferably in the range of1 to 50 g/L, more preferred 5 to 40 g/L and most preferred in the rangefrom 10 to 30 g/L.

Preferably the thus produced suspension is agitated for 5 min to 48 hminutes at a temperature from 1° C. to 100° C. by overhead shaking orstirring. Thus, a not yet delaminated, but delamination agent treatedlayered silicate is obtained as a suspension. In some cases it might benecessary to repeat this procedure several times, e.g. up to 5 times, toobtain a fully treated layered silicate. Details are given in theexample section of the present invention.

Finally, in a second step, the thus treated layered silicate obtained inthe first step is contacted with an aqueous medium, preferably of lowionic strength such as purified water, to produce single silicatelamellae.

To carry out the second step, preferably the gel produced as above isconcentrated, e.g. by centrifugation (preferably 14 000 g for 40 min);the concentrated gel is preferably resuspended in purified water andcentrifuged again. This is repeated until no halide-ions are detectable.This can be monitored by the silver nitrate test. Alternatively, if noconcentration of the delaminated clay is necessary, the excess ions canbe removed by means of dialysis. The thus obtained product isdelaminated and can either be washed with acetone and dried at about 60°C. or freeze-dried from the aqueous medium. A direct drying of thesuspension is feasible as well (preferably 80° C.), but takessignificantly longer time.

Alternatively, the sample may be directly delaminated by using low ionicstrength of the delamination agent in the range of <0.1 mol/L withoutthe need of a washing step.

Further Subjects of the Invention

The invention further provides a delaminated layered silicate, i. e. thedelamination product obtained by the process according to the invention.

The invention likewise provides the use of the delamination productaccording to the invention in the production of a composite material, acoating material, or as a flameproof barrier or as a diffusion barrier.

For example, a dispersion of the delamination product in a polar solventsuch as water can be used to apply a flameproof or diffusion barrier toa substrate. To that end, the dispersion can be applied to the substrateand then the solvent can be removed, for example by drying.

The invention further provides a composite material comprising orobtainable by using the delamination product obtained according to theprocess of the invention.

It is particularly preferred, if the composite material contains apolymer. In order to produce polymer composites, the delaminationproduct can in particular be incorporated into any conventional polymerswhich have been produced by polycondensation, polyaddition, radicalpolymerisation, ionic polymerisation and copolymerisation. Examples ofsuch polymers are polyurethanes, polycarbonate, polyamide, PMMA,polyesters, polyolefins, rubber, polysiloxanes, EVOH, polylactides,polystyrene, PEO, PPO, PAN, polyepoxides. Incorporation into polymerscan be carried out by means of conventional techniques such as, forexample, extrusion, kneading processes, rotor-stator processes(Dispermat, Ultra-Turrax, etc.), grinding processes or jet dispersionand is dependent on the viscosity of the polymers.

In the following the invention is further explained by means ofexamples.

Examples Preparation of Synthetic Layered Silicates by Melt Synthesis

Preparation of[Na_(0.75)]^(inter)[Mg_(2.25)Li_(0.25)]^(octa)[Si₄]^(tetra)O₁₀F₂ (Na075;Vermiculite Type)

For melt synthesis, 4.064 g of NaF (99.995%, Alfa Aesar), 2.511 g of LiF(>99.9%, ChemPur), 2.010 g of MgF₂ (>99.9%, ChemPur), 10.402 g of MgO(99.95%, Alfa Aesar) and 31.014 g of SiO₂ (Merck, fine granular quartz,purum) are weighed in a molybdenum crucible.

The crucible was sealed gas tight by welding under high-vacuum (<10⁻⁴mbar). The crucible was ramped to 1750° C. (15° C./min), held at thistemperature for 70 min, cooled to 1300° C. (55° C./min) and to 1050° C.(10° C./min). Finally, it was quenched by switching of the power. Themilled powder (mill: Retsch PM 100, 250 turns per minute for 20 minutes)was heated at 250° C. and <10⁻′ mbar, transferred into a molybdenumcrucible which was sealed gas tight by welding under high-vacuum (<10⁻⁴mbar). To obtain Na075 the crucible was annealed at 1045° C. for 6weeks.

Preparation of[Na_(0.50)]^(inter)[Mg_(2.5)Li_(0.5)]^(octa)[Si₄]^(tetra)O₁₀F₂ (Na050;Hectorite Type)

For melt synthesis, 2.719 g of NaF (99.995%, Alfa Aesar), 1.680 g of LiF(>99.9%, ChemPur), 4.035 g of MgF₂ (>99.9%, ChemPur), 10.440 g of MgO(99.95%, Alfa Aesar) and 31.127 g of SiO₂ (Merck, fine granular quartz,purum) are weighed in a molybdenum crucible.

The crucible was sealed gas tight by welding under high-vacuum (<10⁻⁴mbar). The crucible was ramped to 1750° C. (15° C./min), held at thistemperature for 70 min, cooled to 1300° C. (55° C./min) and to 1050° C.(10° C./min). Finally, it was quenched by switching of the power. Themilled powder (mill: Retsch PM 100, 250 turns per minute for 20 minutes)was heated at 250° C. and <10⁻′ mbar, transferred into a molybdenumcrucible which was sealed gas tight by welding under high-vacuum (<10⁻⁴mbar). To obtain Na050 the crucible was annealed at 1045° C. for 6weeks.

Preparation of Charge Reduced Hectorite (LCR; Hectorite Type)

Clays of low layer charge <0.48 p.f.u. might not be accessible via meltsynthesis as described above due to immiscibility gaps. The synthesis oflow layer charged clays is carried out by so-called “charge reduction”as follows.

5 g of Na050 were exchanged 7 times with 400 mL of 2 M MgCl₂-solution.The resulting Mg-exchanged hectorite was washed with water till chloridetest (AgNO₃) of the supernatant solution was negative. The slurry wasdried at 80° C. The dried powder was heated at 250° C. for 24 h. (Breuet. al., Langmuir 2012, 28, 14713-14719); the obtained sample is namedLCR.

Preparation of Further Charge Reduced Hectorite (LCR′; Hectorite Type)

2 g of LCR were exchanged 7 times with 400 mL of 2 M MgCl₂-solution. Theresulting Mg-exchanged hectorite was washed with water till chloridetest (AgNO₃) of the supernatant solution was negative. The slurry wasdried at 80° C. The dried powder was heated at 250° C. for 24 h. (Breuet. al., Langmuir 2012, 28, 14713-14719); the obtained sample is namedLCR′.

Characterization of the Synthetic Layered Silicates Cation ExchangeCapacity (CEC)

The CEC was determined according to DIN EN ISO 11260:2017-04 usingbarium chloride.

The determined CECs are 185 meq/100 g (Na075), 129 meq/100 g (Na050),103 meq/100 g (LCR), and 75 meq/100 g (LCR′).

Layer Charge Determination According to Lagaly (L_(c))

The layer charge density per formula unit Si₄O₁₀F₂ (p.f.u.) wasdetermined experimentally by the method of Lagaly (see A. R. Mermut, G.Lagaly, Clays Clay Miner. 2001, 49, 393-397) where interlayer ions areexchanged with n-alkylammonium (C_(n)H_(2n+1)NH₃ ⁺). The d-spacing ofthe resultant intercalation compounds (d₀₀₁) is measured by means ofPowder X-ray diffraction (PANalytical X'Pert Pro, Cu K□-radiation).

For these organo-cations the equivalent area per charge is known for adense packing of either mono- (d=13.3 Å) or bilayers (d=17.6 Å). Theonset of the transition of mono- to bilayer- or from bilayer topseudo-trilayer arrangement with increasing chain length was convertedinto upper limits of charge densities (per formula unit Si₄O₁₀F₂,p.f.u.).

For highly charged Na075 n=9 represents the longest alkyl ammonium chainthat is still capable to balance the charge density in a bilayer(d₀₀₁=17.6 Å) and would correspond to a layer charge of 0.73 p.f.u. fora densely packed bilayer. Upon slightly increasing the equivalent areato n=10 some pseudo-trilayers have to be mixed in to warrant chargebalance as evidenced by a shift of the d-spacing (d=19.2 Å) which wouldcorrespond to a layer charge of 0.67 p.f.u. for a densely packedbilayer. For the sake of simplicity we use the arithmetic mean x=0.70p.f.u. A flat lying monolayer arrangement with even shorter chains isnot feasible for such high layer charges.

In a similar way, for the lower charged clays, the charge densities werederived from the transition of mono- to bi-layers with limiting chainlength.

Na050: n=5 (corresponding to x=0.56 p.f.u.) yields d₀₀₁=13.4 Å, n=6(corresponding to x=0.50 p.f.u.) leads to d₀₀₁=14.2 Å. The layer chargeis hence x=0.53 p.f.u.

LCR: n=8 (corresponding to x=0.40 p.f.u.) yields d₀₀₁=13.4 Å, n=9(corresponding to x=0.36 p.f.u.) leads to d₀₀₁=14.2 Å. The layer chargeis hence x=0.385 p.f.u.

Calculation of the Charge Equivalent Area (A_(s))

The charge equivalent area A_(s) of the layered silicates can becalculated from their layer charge L_(c) by using the following formula(III)

A _(s)=47.6 Å²/(2 L _(c))  (III),

wherein L_(c) is the layer charge as determined above.

The factor of “2” is due to the circumstance that the L_(c) is given performula unit (p.f.u.) of Si₄O₁₀F₂ and each unit cell contains 2 formulaunits.

The multiplier 47.6 Å² results from the typical (a,b)-dimensions of acell of the layered silicates as used herein (a=5.24 Å and b=9.08 Å) andis used for all layered silicates irrespective of the exact celldimensions which e.g. can be determined by Powder X-ray diffraction(PXRD) patterns recorded on a STOE Stadi P powder diffractometer usingCu Kai radiation on samples placed in a glass capillary. Prior tomeasurement the samples are equilibrated for one week over a saturatedK₂CO₃-solution (43% relative humidity).

The following Table 1 shows the synthetic layered silicates as preparedand characterized above and their characteristics as defined in thepresent invention.

TABLE 1 Synthetic Layeres Silicate L_(c) A_(s) Na075 0.70 34.0 Na0500.495 48.1 LCR 0.385 61.8

Characterization of the Delamination Agents Calculation of the ChargeEquivalent Area (A_(d))

The charge equivalent area (A_(d)) of the cationic delamination agentswas determined using the Geometrical Descriptor Plugin of the onlinesoftware (https://chemicalize.org), the structure was then optimized bythe implemented MMFF94 force field. By projection optimization themaximum projection area of the lowest energy conformer, based on the vander Waals radius was obtained. This value (in Angstrom-square Å²) waschosen to be A_(d) of the delamination agent as Å²/charge. By thismeans, the used organo-cations along with their anion have been drawnwith a flat lying conformation. It might be noted, that the anioncontributes only negligible to the obtained A_(d) in case small anionslike halide ions are used.

The following Table 2 shows the delamination agents used and theircharacteristics as defined in the present invention.

TABLE 2 Positively Charged Delamination Agent Atom n_(f) n_(c)n_(c)/(1 + n_(f)) n_(t) A_(d) trimethylammoniumethyl N 1 9 4.50 12 60.4methacrylate iodide* diethylamino ethanol N 1 6 3.00 9 41.1hydrochloride* 2-amino-2-(hydroxy- N 3 4 1.00 8 39.0methyl)-1,3-propanediol hydrochloride* glucosamine N 5 6 1.00 12 56.3hydrochloride N-methyl-D-glucamine N 5 7 1.17 13 59.8 hydrochloride *notaccording to the inventionRelation between the Charge Equivalent Areas A_(d) and A_(s)

In Table 3 the ratio of the charge equivalent areas A_(d) and A_(s) isshown.

TABLE 3 A_(d)/A_(s) Delamination Agent Na075 Na050 LCRtrimethylammoniumethyl 1.78 1.26 0.98 methacrylate iodide* diethylaminoethanol 1.21 0.85 0.67 hydrochloride* 2-amino-2-(hydroxy- 1.15 0.81 0.63methyl)-1,3-propanediol hydrochloride* glucosamine 1.66 1.17 0.91hydrochloride N-methyl-D-glucamine 1.76 1.24 0.97 hydrochloride *notaccording to the invention

Process of Delamination According to the Invention Preparation ofAqueous Solutions of Delamination Agents

Diethylamino ethanol (DEA, >99.5%, Aldrich),2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS, >99%, Aldrich),N-methyl-D-glucamine (Meglumine, >99.0%, Aldrich) were dissolved inpurified water and were titrated to a pH of approximately 8 using HCl(32 wt %) and titrated to pH=7 using 1 M HCl. The solutions were dilutedwith purified water to yield 1M solutions.

2-(Dimethylamino)ethyl methacrylate (DMAEMA, 98%, Aldrich) wasmethylated with methyl iodide resulting in trimethylammoniumethylmethacrylate iodide (TMAEMA iodide): DMAEMA (10 g) was dissolved inacetone (1 L) and methyl iodide was added at a molar ratio of 1.5compared to amino groups. The mixture was stirred overnight. Theprecipitate was washed several times with acetone and finally driedusing high vacuum. Completeness of quaternization was approved by¹H-NMR. TMAEMA iodide was dissolved in purified water to yield a 1 Msolution.

Glucosamine was readily purchased as a hydrochloride (>99.0%, Aldrich).

Glucosamine hydrochloride was dissolved in water to yield a 1M solution.

Treatment of the Layered Silicate with the Delamination Agent in anAqueous Medium

10 mL of 1M solution of the delamination agent correspond to thefollowing molar excess of the delamination agent over the cationexchange capacity of the layered silicate: 27-fold (Na075), 39-fold(Na050), 49-fold (LCR), 67-fold (LCR′).

200 mg of the respective layered silicate was suspended in 10 mL of a 1M solution of the delamination agent in water. The procedure wasrepeated 5 times. After each of the five times, a solid-liquidseparation was carried out. The samples were centrifuged (8,000 g; 10minutes) and the supernatant solution was discarded and replaced byfresh 1 M solution of the delamination agent in water. Finally, theobtained organo clays were washed free of halide ions by washing withpurified water, the absence of halide-ions was proven by thewell-established silver nitrate test with the separated supernatantsolution. Thereby, solid-liquid separation during the washing procedurewas carried out by centrifugation (14,000 g; 40 minutes). This reductionof the ionic strength allows osmotic swelling for all suitabledelamination agents, thereby leading to the formation of single silicatelamellae and gel formation.

For better further processing, it is possible to separate and wash thethus produced product one time with acetone and to dry it at an elevatedtemperature, e.g. at 60° C. The obtained solid product can beresuspended in purified water in a larger weight percentage range.

Characterization of Layered Silicates Treated with the DelaminationAgent

Characterization of Delaminated Gels by SAXS

Small angle X-ray scattering (SAXS) might be used to determine thed-spacing of a delaminated gel. Typically, due to delamination thesed-spacings are >100 Å. SAXS data were measured using a “Double GaneshaAIR” system (SAXSLAB, Denmark). The X-ray source of thislaboratory-based system is a rotating anode (copper, MicroMax 007HF,Rigaku Corporation, Japan) providing a micro-focused beam. The data arerecorded by a position sensitive detector (PILATUS 300K, Dectris).Samples of delaminated organo-clays were prepared by adding a definedamount of ultrapure water to the dry treated layered silicates, leadingto gel-formation. After equilibration for one week SAXS-patterns wererecorded in 1 mm glass capillaries. In contrast, non-delaminatingsamples do not form gels: upon addition of water the non-delaminatingorgano-clay forms sediment. In that case the position of the capillarywas adjusted to ensure the sediment to be in the beam focus during themeasurement. The d-spacing of non-delaminated organo-clays is basicallyindependent on the solid content of the sample, in contrast todelaminating organo-clays, were the solid content of such gel-likesuspensions determines the d-spacing. The results are shown in Table 4.The percentage values given in round brackets are the amounts of treatedlayered silicate in the respective suspensions.

TABLE 4 d₀₀₁-spacing (SAXS) Na075 Na050 LCR Delamination Agent (L_(c) =0.71) (L_(c) = 0.50) (L_(c) = 0.39) trimethylammoniumethyl 187 Å 16.8 Å14.0 Å methacrylate iodide (23 wt %) (20 wt %) (20 wt %) diethylaminoethanol 131 Å 13.6 Å 13.6 Å hydrochloride (20 wt %) (20 wt %) (20 wt %)2-amino-2-(hydroxy- 150 Å 13.9 Å 13.9 Å methyl)-1,3-propanediol (20 wt%) (20 wt %) (20 wt %) hydrochloride glucosamine 138 Å 129 Å 125 Åhydrochloride (20 wt %) (20 wt %) (20 wt %) N-methyl-D-glucamine 140 Å132 Å 133 Å hydrochloride (20 wt %) (19 wt %) (19 wt %)

As shown in the following Table 5 (Delamination Chart), which is inaccordance with the above Table 4, only the delamination agentsfulfilling all mandatory requirements as set out above, showed adelamination of the respective layered silicates (“+”) over a broadrange of layer charges, while the other delamination agents partiallyfailed (“−”).

TABLE 5 Delamination Chart Na075 Na050 LCR Delamination Agent (L_(c) =0.71) (L_(c) = 0.50) (L_(c) = 0.39) trimethylammoniumethyl + − −methacrylate iodide* diethylamino ethanol + − − hydrochloride*2-amino-2-(hydroxy- + − − methyl)-1,3-propanediol hydrochloride*glucosamine + + + hydrochloride N-methyl-D-glucamine + + + hydrochloride*not according to the invention

Furthermore, LCR was used to produce a further charge reduced layeredsilicate LCR′ by further ion exchange with MgCl₂ by repeating the ionexchange procedure in the same manner as described above. The thusobtained LCR′ had a layer charge L_(c) of 0.30 corresponding to a chargeequivalent area A_(s) of 79.3 Å²/charge. Even this layered silicate wasdelaminated by glucosamine hydrochloride and N-methyl-D-glucaminehydrochloride, which fulfill the mandatory requirements on a universaldelamination agent as set out above.

This finding is also particularly interesting for layered silicateshaving a heterogeneous distribution of layer charges in the material.Therefore, for layered silicates, which are known to possess aheterogeneous distribution of layer charges, it is most preferable touse the delamination agents as defined above. The same applies formixtures of charge homogeneous layered silicates of different chargedensities.

1. A process for delamination of a layered silicate in an aqueousmedium, the process comprising: treating a layered silicate with anamount of a delamination agent, the amount of the delamination agentbeing at least equal to the cation exchange capacity of the layeredsilicate; and contacting the treated layered silicate with an aqueousmedium, wherein the delamination agent i. is a compound having exactlyone positively charged atom, the positively charged atom being nitrogenor phosphorous; ii. contains n_(f) functional groups including any oneor more of a hydroxyl group, an ether group, a sulfonic acid estergroup, or a carboxylic acid ester group, n_(f) of being a number from 3to 10; iii. comprises a total number of carbon atoms n_(c) being from 4to 12; iv. has a ratio n_(c)/(1+n_(f)) from 1 to 2; v. contains n_(t)atoms including any one or more of carbon, nitrogen, phosphorous,oxygen, or sulfur, n_(t) being ≥greater than or equal to
 9. 2. Theprocess according to claim 1, wherein the layered silicate is asynthetic or naturally occurring 2:1 clay mineral.
 3. The processaccording to claim 1, wherein the layered silicate is a smectite orvermiculite.
 4. The process according to claim 1, wherein the layeredsilicate is represented by general formula (I)[M _(L) _(c) /valency]^(inter)[M ^(I) _(m) M ^(II) ₀]^(octa) [M ^(III)₄]^(tetra) X ₁₀ Y ₂  (I) wherein, M represents metal cations ofoxidation state 1 to 3; M^(I) represents metal cations of oxidationstate 2 or 3; M^(II) represents metal cations of oxidation state 1 or 2;M^(III) represents atoms of oxidation state 4; X represents di-anions; Yrepresents mono-anions; m is less than or equal to 2.0 for metal atomsM^(I) of oxidation state 3; m is less than or equal to 3.0 for metalatoms M^(I) of oxidation state 2; and o is less than or equal to 1.0. 5.The process according to claim 4, wherein M independently represent Li⁺,Na⁺, or Mg²⁺; M^(I) independently represent Mg²⁺, Al³⁺, Fe²⁺ or Fe³⁺;M^(II) independently represent Li⁺ or Mg²⁺; M^(III) is a tetravalentsilicon cation; X is O²⁻; Y independently represent OH⁻, or F⁻.
 6. Theprocess according to claim 1, wherein the delamination agent ii.contains 3 to 8 of the n_(f) functional groups; and/or iii. comprises 4to 10 of the total number of carbon atoms n_(c); and/or iv. has theratio n_(c)/(1+n_(f)) from 1 to 1.8; and/or v. contains 10 or more ofthe n_(t) atoms.
 7. The process according to claim 1, wherein thedelamination agent i. is a compound having exactly one positivelycharged nitrogen atom; and/or ii. contains 3 to 6 of the n_(f)functional groups, the n_(f) functional groups including any one or moreof a hydroxyl group or an ether group; and/or iii. comprises 5 to 9 ofthe total number of carbon atoms n_(c); and/or iv. has the ration_(c)/(1+n_(f)) from 1 to 1.5; and/or v. contains 11 or more of then_(t) atoms.
 8. The process according to claim 1, wherein treating thelayered silicate with the amount of the delamination agent includestreating the layered silicate with an aqueous solution of thedelamination agent, wherein the concentration of the delamination agentin the aqueous solution is high enough to prevent delamination of thelayered silicate while treating the layered silicate with the amount ofthe delamination agent.
 9. The process according to claim 8, wherein theconcentration of the delamination agent in the aqueous solution is from0.2 to 2 mol/L.
 10. The process according to claim 8, wherein theconcentration of the layered silicate in the aqueous solution containingthe delamination agent is in the range from 1 to 50 g/L.
 11. The processaccording to claim 1, wherein when contacting the treated layeredsilicate with the aqueous medium, the aqueous medium has an ionicstrength low enough to cause delamination of the treated layeredsilicate.
 12. The process according to claim 1, wherein the aqueousmedium in the second step includes water.
 13. A delaminated layeredsilicate obtained by a process comprising: treating a layered silicatewith an amount of a delamination agent, the amount of the delaminationagent being at least equal to the cation exchange capacity of thelayered silicate; and contacting the treated layered silicate with anaqueous medium, wherein the delamination agent i. is a compound havingexactly one positively charged atom, the positively charged atom beingnitrogen or phosphorous; ii. contains n_(f) functional groups includingany one or more of a hydroxyl group, an ether group, a sulfonic acidester group, or a carboxylic acid ester group, n ranging from 3 to 10;iii. comprises a total number of carbon atoms n_(c) being from 4 to 12;iv. has a ratio n_(c)/(1+n_(f)) from 1 to 2; v. contains n_(t) atomsincluding any one or more of carbon, nitrogen, phosphorous, oxygen, orsulfur, n_(t) being greater than or equal to
 9. 14-15. (canceled) 16.The process according to claim 5, wherein the layer charge L_(c) isgreater than or equal to 0.28 and less than or equal to 0.95.
 17. Theprocess according to claim 8, wherein the concentration of thedelamination agent in the aqueous solution is in the range of 0.5 to 1.5mol/L.
 18. The process according to claim 8, wherein the concentrationof the layered silicate in the aqueous solution containing thedelamination agent is in the range from 5 to 40 g/L.
 19. The processaccording to claim 8, wherein the concentration of the layered silicatein the aqueous solution containing the delamination agent is in therange from 10 to 30 g/L.
 20. The process according to claim 12, whereinthe water is purified water.